1. Field of the Invention
The present invention relates to a golf ball which even when hit at a relatively low golf-club head speed, acquires a high initial velocity and thus provides improved carry.
2. Related Art
One of the aspects of performance most desired in golf ball development is improved carry.
The Rules of Golf which regulate golf competition include provisions relating to the flight distance of the ball. The initial velocity and overall distance standard are set forth in paragraphs d. and e. of Appendix III. Technical innovations in golf balls are generally developed in keeping with these rules.
A variety of multi-piece golf balls such as three-piece and four-piece balls have been devised. Because most such balls are developed in conformity with the Rules of Golf, they are designed primarily for high head speed players and often fail to provide an acceptable carry when hit by a low head speed player.
An object of the present invention is to provide a solid golf ball having an increased initial velocity regardless of whether the club head speed is low or high, and having in particular an excellent rebound and distance when hit at a low head speed.
Under the circumstances that professional golfers and skilled amateurs are high head speed players, but the majority of golfers have a relatively low head speed, the inventor has succeeded in developing a golf ball that has excellent rebound characteristics so that the ball is highly advantageous to the majority of golfers who have a relatively low head speed.
In a first aspect, the invention provides a solid golf ball of multilayer structure comprising a core, an enclosing layer around the core, and a cover. The core and the enclosing layer have volumes which satisfy the following relationship: 0.05%xe2x89xa6(core volume)/(enclosing layer volume)xc3x97100%xe2x89xa660%. The core has a rebound of A (cm) and the core enclosed with the enclosing layer, referred to as enclosed core, has a rebound of B (cm) both when dropped under gravity from a height of 120 cm, and the rebound of the bare core is smaller than the rebound of the enclosed core, that is, A less than B. Preferably, the core has a diameter of 1 to 16 mm, and the rebound B of the enclosed core is at least 90 cm.
As to the preferred materials of which the respective layers are made, the core is comprised of a thermoplastic resin as a base; and the enclosing layer is comprised of a thermoplastic resin as a base. Typically, the core is formed of a composition comprising 100 parts by weight of a base and up to 40 parts by weight of an inorganic filler. More preferably, each of the core, the enclosing layer, and the cover is formed of a composition comprising 100 parts by weight of a base and up to 40 parts by weight of an inorganic filler.
In a second aspect, the invention provides a solid golf ball of multilayer structure comprising a core, an enclosing layer around the core, and a cover, wherein each of the core, the enclosing layer, and the cover is comprised of a thermoplastic resin as a base. The golf ball may further have an intermediate layer between the enclosing layer and the cover, the intermediate layer being comprised of a thermoplastic resin as a base. More preferably, the core is formed of a composition comprising 100 parts by weight of the base and up to 40 parts by weight of an inorganic filler. Most preferably, each of the core, the enclosing layer, and the cover is formed of a composition comprising 100 parts by weight of the base and up to 40 parts by weight of an inorganic filler.
In one preferred embodiment of the second aspect, the core and the enclosing layer have volumes which satisfy the following relationship: 0.05%xe2x89xa6(core volume)/(enclosing layer volume)xc3x97100%xe2x89xa660%. The core preferably has a diameter of 1 to 16 mm. The core enclosed with the enclosing layer preferably has a rebound of at least 90 cm when dropped under gravity from a height of 120 cm.
The golf ball of the invention has such rebound efficiency that the ball conforms to the rule for initial velocity by delivering a lower initial velocity than the stipulated value at the relatively high head speed range for which the rules are established, yet enables a relatively high initial velocity to be achieved at lower head speeds. That is, the invention provides a golf ball which, based on the deformation that occurs in the relatively high compression range (high head speed players) to which the above rules most directly apply, holds down rebound only in this range while increasing rebound in the low head speed range where most golfers belong, thus providing the average player with better rebound characteristics. The invention achieves a golf ball that is highly advantageous to the majority of golfers who have a relatively low head speed of less than about 42 m/s, and especially less than about 40 m/s.